Here is a summary of all the game improvements and changes since the single player version:

Resource production on planets is adjusted so that asteroid belts and dead planets are more important to control for ore and iridium production (now you basically have to start capturing other planets before you can build a space platform)

Production costs for ships are adjusted to make more powerful ships more than twice the cost of the weaker ones

Repairing ships now costs resources and requires colonies

UI improvements, overall resources are shown at the top of the screen, more detailed stats about each planet are shown on the left.

Tax level reduced a bit (gold production lower) to match adjustments in resource production on planets

Protest levels for citizens disable that worker on the planet

When capturing a planet citizens default to having a protest level so that the planet cannot build back up immediately (this gives opponents a better chance of being able to retake the planet)

In-game chat system for talking to other players

Added game option to "distribute planets evenly" to allow for more variety in where planets are placed on the game grid

Added game option for turn time limit so that turns auto-end after the timer is up

Resources are now generated before population food consumption and starvation at the end of the turn, this reduces "surprise" starvation.

Player points are now assigned as progress towards galactic conquest is achieved.